Creation of glazing comprising an opening

ABSTRACT

The invention relates to a method for preparing a sheet of curved glass comprising an opening involving bending followed by cooling, the periphery of the sheet and the periphery of the opening being supported, at least at the start of cooling, by a skeleton.

The invention relates to a method of creating glazing comprising one ormore opening(s) and that may notably act as a roof of a motor vehicle.

The creation of fixed glass canopies for motor vehicles offers a certainnumber of advantages such as esthetic appearance, cost, transparency,the possibility of fitting the roof with photovoltaic cells, etc. It maybe desirable to add an opening function to this type of canopy byproviding it with a window that can be accessed and opened from insidethe vehicle. That entails knowing how to bend glazing equipped with alarge-sized orifice without said orifice overly weakening it ornoticeably altering its overall curvature, as these would detract fromthe esthetic appearance and functionality of the product and couldproduce optical defects. One of the major difficulties is to guaranteethe close tolerances of the interior opening in relation to the exteriorcontour of the glazing in order to interface with the mobile roof. Inaddition, such glazing has to be sufficiently resistant to the forcesexerted by the wind (known as the “wind load”) which apply a heavy loadthereto when driving along with the roof open or closed. It has also tobe able to withstand a load such as one meter of snow. Another type ofloading is the torsional effects which occur for example when one wheelof the vehicle is resting up on a sidewalk or when sharply mounting thekerb. It has been found that tensile stresses appear in the corners ofthe opening in the roof when the glazing is subjected to any kind ofmechanical force.

U.S. Pat. No. 5,974,834 teaches how to bend and temper glazingcomprising a small-sized hole, essentially for making holes in the backwindow of motor vehicles. Such a hole in a back window is essentiallyused for attaching an aerial or a stop light, which means that its areais of the order of 0.006 m² at most. Individual sheets of glass are bentunder gravity on a frame comprising an additional support for the borderof the orifice. This additional support is notched at its edge (as alsotaught in WO93/02017 or U.S. Pat. No. 5,118,335 regarding the externalborder of an unholed glazing) to make the edge of the glass moreaccessible to the annealing air. The edge of the glazing is supposed tosit right in the middle of the notching as shown in FIG. 5 of U.S. Pat.No. 5,118,335. According to U.S. Pat. No. 5,974,834, the support mayalso be a solid metal plate of larger area than the orifice so as tosupport the edges of the orifice during bending and tempering. A motorvehicle back window bending frame generally has a contact width of morethan 5 cm.

Tests carried out by the applicant have demonstrated that this type ofsupport for the edges of the opening is unable to lead to glazing thatis sufficiently robust, particularly for “canopy with in-built sunshineroof” applications. In particular, a notched support appears to lead toa succession of compressions and tensions in the border of the glazing,which in fact weakens it considerably and what is more gives rise toprohibitive optical defects.

In the context of the present invention, in order to give the border ofthe opening sufficient strength, it has been decided that a ring ofcompression should be conferred upon it, this meaning that the extremeedge of the opening is systematically under compression for the entireperimeter of the opening. In addition, attempts have been made to givethis compression a high value of at least 4 MPa, and preferably at least6 MPa, and more preferably still at least 8 MPa, and even morepreferably still, at least 9 MPa at any point on the perimeter of theopening. These values relate firstly to the sheet of glass in contactwith the exterior surroundings of the motor vehicle and preferably alsoto the other sheet or sheets contained in the laminated glazing, andtherefore also relate to the arithmetic mean of the stress values forall the sheets of the glazing.

In order to achieve this objective, it has been found that the supportfor the border of the opening, at least at the time that cooling begins,was advantageously continuous (or linear, as opposed to “notched” as inU.S. Pat. No. 5,974,834) and parallel to the edge of the glazing. Whatthat means is that at every point on the border of the support of theopening, the tangent to the support never crosses into said support,unlike the situation with the “notched” frame of the prior art. Inaddition, the support of the opening has to be relatively slender and bepositioned a few mm, generally at least 2 mm and even at least 3 mm,away from the edge of the opening of the glazing it supports at the endof supporting. This type of support is often known by the term“skeleton”. A skeleton is a thin strip of metal having one of its edgefaces facing upward to support the glass, the thickness of said edgeface generally ranging from 1 to 5 mm and more generally from 2 to 3.5mm. At the end of bending, the skeleton is in continuous contact on theedge face with the glass (for the bending step that involves thatparticular skeleton). The skeletons are preferably coated with a fibrousmaterial of the felt type or web of metal and/or ceramic refractoryfibers, as is well known to those skilled in the art. These felts reducethe marking of the glass. This fibrous material generally has athickness ranging from 0.3 to 1 mm.

Like the border of the opening, the exterior (or external) border of theglazing also preferably has a ring of compression of at least 4 MPa, andpreferably at least 6 MPa, and preferably at least 8 MPa, and morepreferably still, at least 9 MPa at any point on the perimeter of thesheet of glass. In order to achieve these values, the periphery of thesheet is supported by a skeleton at least at the start of cooling thathas already been explained in respect of the opening. These valuesrelate first of all to the sheet of glass in contact with the exteriorsurroundings of the motor vehicle (and therefore the sheet directly incontact with the skeleton) and preferably also relate to the other sheetor sheets contained in the laminated glazing, and therefore also to thearithmetic mean of the values of stress in all the sheets of theglazing.

The method according to the invention involves bending followed bycooling. Bending is performed at least in part, if not in full, on abending skeleton, both at the border of the opening and at the exteriorborder of the glazing. According to the invention, bending is performedat least partially under gravity on a bending skeleton supporting theperiphery of the sheet and the periphery of the opening.

The cooling is performed at least to start off with, on the skeleton,both at the border of the opening and at the exterior border of theglazing. The skeleton that supports the glass at the start of cooling isknown as the “final skeleton”, it being understood that this finalskeleton may also be a bending skeleton and, in particular, the lastbending skeleton in contact with the glass in cases where multipleskeletons are used. Thus, the entire bending and cooling operations maybe formed on the same skeleton.

Thus, the invention relates first of all to a method for preparing asheet of curved glass comprising an opening involving bending followedby cooling, the periphery of the sheet and the periphery of the openingbeing supported, at least at the start of cooling, by a skeleton (knownas the “final” skeleton).

Advantageously, the final skeleton lies a distance away from the edge ofthe opening of the sheet with which it is in contact, of at least 2 mmand more generally at least 3 mm, for example at least 5 mm, at least atthe start of cooling, that is to say with the final form of the sheet.The final skeleton is, at least at the start of cooling, in continuouscontact with the glass along the edge face.

The method according to the invention is well suited to glazings of allsizes, even those of large size that may act as motor vehicle roofs.What is meant by large-sized glazing is glazing of which one facemeasures more than 0.8 m², or more than 1 m², or even more than 2 m² (ofcourse, this refers to the total area of one main face comprising thesurface area of glass plus the surface area of any opening). Large-sizedglazings are particularly heavy and one might have thought that thesupports would have left marks. This fear is all the more keenly feltsince, in the case of a laminated glazing, the two sheets are bent atthe same time, superposed on the bending support. The weight thereforeincreases very quickly with the increase in size of the glazing, all ofwhich tends toward an increase in the risk of marking. While having anopening in the glazing in itself leads to production difficulties interms of bending and in terms of a reduction in the mechanical strengthof the final glazing, paradoxically a larger opening may have advantagesif the choice has been taken to support the periphery of the openingduring the bending and at the start of cooling. Specifically, a) thelarger the opening, the greater the reduction in the weight of theglazing, which tends toward a reduction in marking, and b) the largerthe opening, the longer its perimeter and therefore the longer theperimeter support surface, which means that the glazing is spread over alarger support surface area, again tending toward a reduction inmarking. Thus, for preference, the opening has an area in excess of 0.03m² and even in excess of 0.05 m² and even in excess of 0.08 m² and evenin excess of 0.1 m² and even in excess of 0.2 m² and generally in excessof 0.3 m². In general, the opening has an area smaller than 1 m². Forpreference, the opening has an area greater than 5% or even greater than10% of the total area of the glazing (of course the total area of asingle main face comprising the surface area of glass plus that of theopening). In general, the opening has an area of less than 80% or evenof less than 50% of the total area of the glazing.

It has been possible to demonstrate that too small a size of opening(measuring less than 0.03 m²) was not favorable to the cooling of theborders of the opening which meant that the desired edge stresses couldnot be achieved. Specifically, it would seem that too small an openingleads to a mass effect that is prejudicial to effective cooling becauseof the large mass of glass surrounding the opening. The larger theopening, the more the cooling occurs in a similar way to the coolingconferred upon the exterior borders of the glazing, which means that thelast support of the border of the opening at the start of cooling canactually be effected using a support of the skeleton type without thathaving detrimental consequences on edge stresses.

The cooling may be performed on superposed sheets in which case it isrelatively slow. In such cases, the temperature of the glass is loweredbelow the gravity bending temperature down to 480° C. at a controlledrate generally less than 3° C. per second and generally greater than0.2° C. per second. Below 480° C., it is possible to blow onto the glassto accelerate the cooling. The superposition of the sheets does notimpede the obtaining of the desired edge stresses on each of the sheetsconsidered individually. The cooling may be more rapid to the point ofconstituting semi-tempering, in which case this cooling is performedindividually, sheet by sheet, rather than with the sheets superposed. Inthis case, the temperature of the glass is lowered below the gravitybending temperature down to 480° C. at a rate generally in excess of 10°C. per second and generally less than 150° C. per second. In all cases,cooling commences while the glass is still in contact with the finalskeleton and this cooling is performed sufficiently rapidly to obtainthe ring of compression with the desired compressive stress value (atleast 4 MPa) at least in the case of the sheet of glass in directcontact with the skeleton and preferably for the other sheet (or sheets)juxtaposed thereon. The more rapidly the cooling is carried out, thegreater the extent to which the compressive stress in the ring ofcompression is increased. That is true of the edge of the opening and ofthe exterior edge of the glazing.

According to the invention, the method may be applied to two sheets thatare superposed during bending and cooling, or even to more than twosheets.

For sheets intended to be assembled within one and the same laminatedglazing, the bending itself may be performed simultaneously on saidsuperposed sheets. This bending may also be performed sheet by sheet(individual sheets not superposed) when the final step of bending isperformed by pressing against a solid form. In all cases, however, it ispreferable for at least the start of cooling to be carried out on thefinal skeleton when these sheets intended to be assembled aresuperposed.

For preference, the perimeter of the opening does not have a radius ofcurvature smaller than 15 mm and for preference no radius of curvaturesmaller than 60 mm, for example no radius of curvature smaller than 80mm. The perimeter of the opening therefore has, at all points, a radiusof curvature of at least 15 mm and preferably of at least 60 mm, forexample of at least 80 mm. The opening may, for example, be circular orof the quadrilateral type with radiused corners as has already beenstated. This feature relating to the radii of curvature is particularlyfavorable to the integrity of the glazing when subjected to torsion andtensile stresses in the corners.

The invention also relates to a method of gravity bending a sheet ofglass (which covers the possibility of having several sheets of glasssuperposed, notably two of these) comprising an opening (which coversthe possibility of having several openings in one and the same glazing),the periphery of the opening being supported during bending by a bendingskeleton.

The bending skeleton comprises a part supporting the periphery of theglazing (or “exterior” or “external” periphery) and a part supportingthe periphery of the opening. The same is true of the final skeleton.

That part of the skeleton that supports the opening may be fixed orarticulated or multiple. For preference, this part is modified duringbending so that its concavity when viewed from above increases duringthe course of bending. This modification in shape allows it better tofollow the change in curvature during the course of bending so that theweight of the glass is spread over a larger support surface area forlonger. This then reduces the tendency to marking and reduces the riskof reverse bending (the local formation of curvature in the oppositedirection to the desired curvature). The increase in the concavity ofthe skeleton may be obtained using an articulated or multiple skeleton.An articulated skeleton is equipped with several parts articulatedtogether and the geometry of which is modified during the course ofbending. For preference, articulation is made to occur progressively(rather than suddenly) during the course of the bending.

A multiple skeleton comprises several single skeletons (generally two)with different concavities, which one after the other (the more concaveone after the less concave one, when viewed from above) supportsubstantially the same line of support (or lines that are very closelyadjacent, and juxtaposed). The bending skeleton that is the first tosupport the glass is often known as the “roughing” skeleton and thebending skeleton that supports the glass last is known as the“finishing” skeleton.

That part of the bending skeleton that supports the exterior border ofthe sheet may be of the same type as the one used to support the borderof the opening, or a different type. In all the cases, it is of thesimple, articulated or multiple type. The type of skeleton is to bechosen according to the complexity of the shape of the sheet and as afunction of the tolerances on the dimensions.

If the geometry of the sheet is difficult to achieve (pronouncedcurvatures in all directions and/or close tolerances), a skeleton thetwo parts of which are of the multiple type is advantageously used byway of skeleton supporting the exterior border and the border of theopening. In the case of multiple double skeleton parts, these eachcomprise (the one for the external edge and the one for the edge of theopening) two simple skeletons with different curvatures which supportthe glazing one after the other, the skeleton with the less pronouncedcurvature supporting the glazing first.

In all cases, the last shape of the bending skeleton completely conformsto the glass both at the periphery of the opening and at the peripheryof the sheet. The same is true of the final skeleton in contact with theglass at the start of cooling.

The final skeleton supporting the edge of the opening has a shapesubstantially identical to the opening in the sheet with which it is incontact, while at the same time observing a setback (“d” in FIG. 2 a) ofa few mm, generally at least 2 mm, or even at least 3 mm at the start ofcooling, that is to say when the sheet is fixed in its final form bycooling (the sheets are therefore bent at that time, a fact which is notdepicted in FIG. 2 a). The skeleton supporting the edge of the openingtherefore generally has the same shape as the opening, enlarged by themagnitude of the setback “d” around its entire perimeter. The skeletonfollows the shape of the opening over its entire perimeter, keepingsubstantially the same distance back from the edge of the opening.

The opening in the glass does not come too close to the exterior borderof the glazing because that could overly weaken it, particularly duringhandling operations. Thus, the opening is at least 50 mm and preferablyat least 100 mm, or even at least 150 mm away from the exterior borderof the glazing.

The opening is generally made on the individual sheets before they arebent, and therefore when they are in the flat state. The opening isgenerally cut out using pressurized water jets. The cut edges (theexternal edge just like the edge of the opening) are subjected tosuitable shaping between the cutting-out step and the bending step.

Before being combined into laminated glazing, one or more of the sheetsintended to form such laminated glazing may be coated with enamel. Inthe case of a motor vehicle canopy combining two sheets of glassseparated by a layer of polymer such as polyvinyl butyral (PVB), enamelmay be applied notably to the concave face (therefore the one facingtoward the interior of the vehicle) of one or other of the two sheets.This enamel is applied to the glass before it is bent.

The bending may be performed on the sheets considered individually or onthe sheets in the superposed state. In all cases, gravity bending isperformed with a glass at a temperature ranging between 600 and 700° C.and preferably between 550 and 650° C.

Gravity bending on a skeleton may be a preliminary bending step that isfollowed by a press bending step pressing against a concave or convexsolid form. This compression bending is generally performed at between600 and 620° C. In this case, in order to get back to the desired edgecompression values (of at least 4 MPa) after compression bending, theborders of the glass (the exterior edge and the edge of the opening) arerested on the “final skeleton” in the hot state (glass temperature:between 600 and 700° C. and preferably between 550 and 650° C.) andcooling is begun while the glass is resting on this final skeleton. Itis in fact contact between the border of the glass and the finalskeleton at the start of cooling which causes the excellent observededge compression. Cooling is performed in the ways already indicatedabove according to whether there is a desire for the glass to besemi-tempered or not.

If the gravity bending is performed with two sheets superposed, thesheet on the top may have an opening slightly larger than the one on thebottom, which means that the border of the sheet on the top willeverywhere be set back a little with respect to the border of the sheeton the bottom, this setback (“x” in FIG. 7) preferably ranging between 0and 15 mm, notably 3 and 10 mm. This offsetting of the openings in thetwo sheets makes it possible to ensure slightly more effective coolingof the bottom sheet which will then see an increase in its edgestresses. This bottom sheet during bending will become the top sheet ofthe motor vehicle canopy and it may be desirable for it to haveparticularly high edge stresses.

The sheets of glass to which the present invention relates generallyhave a thickness ranging from 1 to 4 mm.

FIG. 1 represents the type of glazing to which the present inventionrelates. This is laminated glazing 1 comprising two sheets of glassbetween which there is inserted a thin layer of polymer of the PVB type.This glazing is curved and has an opening 2 the surface area of whichrepresents approximately 20% of the total surface area of the glazing.This glazing has two main faces. This glazing may act as a motor vehiclesunshine roof, it being possible for the opening to be equipped with anarticulated flap. This glazing comprises an exterior border 3 and theopening 2 comprises a border 4. The opening 2 has a perimeter of thequadrilateral type, with the four corners having fairly large radii ofcurvature r.

FIG. 2 a) depicts, in cross section, two superposed sheets of glasscarried by a support 10 of the skeleton type covered with a felt 11 ofrefractory fibers. The skeleton is at a distance d (“set back”) from theedge of the glass. FIG. 2 b) depicts the resulting distribution ofstresses in each of the final sheets. This diagram corresponds to ameasurement of the inbuilt stresses using the “sharples”, measurementtools commonly used by those skilled in the art for measuring stresses.It may be seen that the extreme edge of the sheets of glass iscompletely in compression because the part 12 of the stress curve isnegative and therefore in the compression domain. By contrast, the zoneof the glass which was just above the support 10 is in tension, becausethe part 13 of the stress curve is positive.

FIG. 3 depicts a device for gravity bending sheets of glass comprising atwo-part double skeleton, one part (31, 33) for supporting the peripheryof the sheets of glass and one part (32, 34) for supporting theperiphery of the opening. Each component 31, 32, 33 and 34 is a simpleskeleton in itself. In FIG. 3 a) it is the roughing skeleton that is inthe uppermost position, that is to say both, on the one hand, theroughing skeleton that supports the periphery of the glazing and, on theother hand, the roughing skeleton that supports the periphery of theopening. The finishing skeletons 33 and 34 for the periphery of theglazing and for the periphery of the opening respectively, are in thelowermost position, with no possible contact with the glass. After acertain bending time, the roughing skeletons are lowered gradually andthe glass (which has not been depicted) finds itself supported by thefinishing skeletons 33 and 34 as depicted in FIG. 3 b). In actual fact,the roughing skeletons 31 and 32 are connected to one another by fixedconnections and the finishing skeletons 33 and 34 are also connected toone another by fixed connections. The switch from the roughing skeletonsto the finishing skeletons is very gradual and performed by virtue of adevice like the one depicted in FIGS. 1 to 5 of WO2007/077371.

FIG. 4 shows the relative movement of the two pairs of skeletons, thepair of roughing skeletons (31, 32) and the pair of finishing skeletons(33, 34) during the bending of a sheet of glass 1 provided with anopening 2. In FIG. 4 a) the sheet of glass 1 provided with an opening 2rests on the pair of roughing skeletons, the roughing skeleton 31supporting the periphery of the sheet and the roughing skeleton 32supporting the periphery of the opening 2. In FIG. 4 b) the sheet ofglass 1 provided with an opening 2 rests on the pair of finishingskeletons, the finishing skeleton 33 supporting the periphery of thesheet and the finishing skeleton 34 supporting the periphery of theopening 2. The roughing skeleton 31 and the roughing skeleton 32 aresecured to one another because of their fixed connections 35. Thefinishing skeleton 33 and the finishing skeleton 34 are secured to oneanother because of their fixed connections 36.

FIG. 5 depicts an articulated skeleton that can be used to support theglass around the opening. This skeleton comprises two articulatedlateral parts that can be raised during bending. It is considered thatthis movement causes an overall increase in the curvature or concavity(when viewed from above) of the skeleton. The skeleton that comes intocontact with the periphery of the glazing is not depicted here.

FIG. 6 depicts an articulated multiple skeleton comprising a simplefirst skeleton 5 for supporting the perimeter of the opening at thestart of bending, two articulated lateral parts 8 and 9 that can beraised during the course of bending. It is considered that this movementincreases the overall curvature or concavity (when viewed from above) ofthe skeleton. The skeleton which comes into contact with the peripheryof the glazing is not depicted here.

FIG. 7 depicts two sheets of glass 41 and 42 which are superposed duringbending (the support skeletons are not depicted), the top sheet 41having a slightly larger opening 43 than the bottom sheet 42, so thatthe border of the top sheet is everywhere set back from the border 44 ofthe bottom sheet by x mm. This offsetting of the openings of the twosheets ensures slightly more effective cooling of the bottom sheet whichthen sees an increase in its edge stresses.

1. A method for preparing a sheet of curved glass comprising an opening,the method comprising bending the sheet of glass followed by cooling,wherein a periphery of the sheet of glass and a periphery of the openingtherein are supported, at least at the start of the cooling, by a finalskeleton.
 2. The method of claim 1, wherein the final skeleton comprisesa linear strip of metal having one of its an edge face facing upward tosupport the sheet of glass.
 3. The method of claim 2, wherein athickness of the edge face ranges from 1 to 5 mm.
 4. The method of claim1, wherein the bending is performed at least partially under gravity ona bending skeleton supporting the periphery of the sheet of glass andthe periphery of the opening.
 5. The method of claim 4, wherein aconcavity of a part of the bending skeleton that supports the peripheryof the opening increases during the bending.
 6. The method of claim 5,wherein the part of the bending skeleton that supports the periphery ofthe opening comprises two skeletons which support the opening, one afterthe other, during the bending.
 7. The method of claim 1, wherein thefinal skeleton lies a distance away from an edge of the opening of atleast 2 mm at least at the start of the cooling.
 8. The method of claim7, wherein the final skeleton has the shape of the opening around itsentire perimeter keeping substantially the same distance away from theedge of the opening.
 9. The method of claim 1, wherein a perimeter ofthe opening has, at all points, a radius of curvature of at least 15 mm.10. The method of claim 9, wherein the perimeter of the opening has, atall points, a radius of curvature of at least 60 mm.
 11. The method ofclaim 1, wherein the cooling is sufficiently rapid enough to obtain acompressive stress value around a border of the opening of at least 4MPa.
 12. The method of claim 11, wherein the cooling is sufficientlyrapid enough to obtain a compressive stress value at the border of theopening of at least 8 MPa.
 13. The method of claim 1, wherein theopening has an area in excess of 0.03 m².
 14. The method of claim 13,wherein the opening has an area in excess of 0.08 m².
 15. The method ofclaim 1, wherein the opening has an area in excess of 5% of a total areaof a main face of the sheet of glass.
 16. The method of claim 1, whereinthe final skeleton is also a bending skeleton.
 17. The method of claim1, wherein a part of a bending skeleton that supports the periphery ofthe sheet of glass comprises two skeletons which support the sheet ofglass, one after the other, during the bending, and a second skeletonthat supports the sheet of glass after a first skeleton has a morepronounced curvature than the first skeleton.
 18. The method of claim 1,wherein two sheets are superposed during the bending and the cooling.19. The method of claim 1, wherein the cooling is sufficiently rapidenough to obtain a compressive stress value around a border of theopening of at least 6 MPa.
 20. The method of claim 1, wherein theopening has an area in excess of 0.1 m².
 21. A method for preparing asheet of curved glass comprising an opening, the method comprisingbending the sheet of glass followed by cooling, wherein a periphery ofthe sheet of glass and a periphery of the opening therein are supported,at least at the start of the cooling, by a final skeleton, a perimeterof the opening has, at all points, a radius of curvature of at least 60mm, the final skeleton comprises a linear strip of metal having an edgeface facing upward to support the sheet of glass, a thickness of theedge face ranges from 1 to 5 mm, the bending is performed at leastpartially under gravity on a bending skeleton supporting the peripheryof the sheet of glass and the periphery of the opening, a concavity of apart of the bending skeleton that supports the periphery of the openingincreases during the bending, the part of the bending skeleton thatsupports the periphery of the opening comprises two skeletons whichsupport the opening, one after the other, during the bending, a part ofthe bending skeleton that supports the periphery of the sheet of glasscomprises two skeletons which support the sheet of glass, one after theother, during the bending, and a second skeleton that supports the sheetof glass after a first skeleton has a more pronounced curvature than thefirst skeleton.